"Earth working" machines are made in a broad variety of machine type and drive system configurations. Two exemplary types of such machines in common use are mining shovels and draglines. Both are used in the process of extracting a valuable resource, e.g., coal, copper ore or the like, from the earth. Mining shovels, also referred to as excavators, and draglines can have a digging dipper or bucket capable of carrying anywhere from about 20 cubic yards (about 16 cubic meters) to about 120 cubic yards (about 100 cubic meters) or more of ore or the like. A leading manufacturer of mining shovels and draglines is Harnischfeger Corporation of Milwaukee, Wis.
A typical earth working machine, e.g., a mining shovel, has a platform supported on the ground by crawler tracks. A machinery "house" or upper portion is mounted on the platform and rotates about an axis of rotation which is vertical when the shovel is on level ground. The drive systems, whether electric, hydraulic or some combination thereof, used to power various functions of the shovel are mounted in the upper portion and one such drive system, often referred to as the "swing" function, causes the above-described rotation.
Extending from the machinery upper portion of a mining shovel is an upwardly, forwardly-pointing angled boom extending along a boom axis and supported by steel cables or lines. In normal operation, the boom angle does not change. A dipper stick or handle extends across and through the boom, is pivotable with respect to such boom and has a digging dipper (in the terminology of the industry) mounted at one handle end. The dipper has forward-pointing teeth which dig into and remove rock, ore or the like when the machine is being used.
An electrical rack-and-pinion type drive is capable of moving the handle (and, of course, the dipper attached to the handle) along an axis toward and away from the boom. This drive is often referred to as the "crowd" function since by using it, the operator can cause the dipper to crowd into a hillside, a pile of rock or the like.
The machine also has a winch for retrieving or paying out steel cable which extends over a rotatable pulley or sheave at the end of the boom and attaches to the dipper. Operation of the winch causes the handle to pivot about an axis on the boom and the winch drive is often referred to as the "hoist" function. Because the dipper can be moved by both the crowd and hoist drives, the dipper (and, notably, the dipper teeth) can be positioned anywhere within a two-dimensional "envelope" in a vertical plane coincident with the boom, the dipper handle and the axis of rotation of the machinery house. And when rotation of the upper portion is considered, the two-dimensional envelope becomes a three-dimensional "spatial" envelope.
A common way of using a mining shovel is to urge the dipper along the surface of the earth so that the dipper teeth are moving forwardly (i.e., away from the machinery house and the platform) and parallel to such surface. In the parlance of shovel manufacturers and users, this is referred to as "keeping grade."
A typical control arrangement has an operator's chair and two control levers, one each for manipulation by the operator's right and left hands, respectively. The right-hand control lever moves forward and backward to move the dipper using the hoist function and moves left and right to pivot the machinery house using the swing function. The left-hand control lever moves forward and backward to control the crowd function.
Commonly, such levers are at the ends of chair arm rests so that the operator need not support arm weight and so that the arms are steadied during lever manipulation. To keep grade or, for that matter, to move the dipper teeth along other paths (i.e., paths other than the single-function linear paths mentioned above), the operator must move the right-hand lever and the left-hand lever forward and backward in coordinated fashion.
Given the configuration of known control apparatus, keeping grade is very difficult. Proper coordinated lever movement to cause the dipper teeth to follow a desired path requires a good deal of skill and practice. The task is made more difficult because lever movement in view of the desired dipper movement is not at all intuitive. For example, the known control arrangement requires two levers to be moved forward and/or backward in some coordinated way, even though the desired path of the dipper teeth is along a horizontal line, i.e., neither forward nor backward.
Accurate dipper path control is certainly not a trivial consideration. A production objective is efficiency, i.e., to provide "three pass" loading of a large haulage truck. That is, the dipper and truck capacities are cooperatively selected so that three dippers full of material will fully load the truck. If the dipper is manipulated in a less-than-optimal way, the dipper will not completely fill on one or more passes and, perhaps, a fourth pass will be needed to completely fill the truck. Time is wasted and given the fact that the shovel and the truck each cost well over a million dollars (in fact, a large mining shovel costs several million dollars), the return on the investment is diminished.
And those are not the only problems attending use of known mining shovels. Another involves shoe and/or dipper damage.
As noted above, a mining shovel is mounted on a platform supported by crawler tracks. Each track is made up of a number of link-type shoes pivotably pinned to one another to form a continuous track. The swing function rotates the machinery house with respect to the tracks and since a mining shovel is several stories high, it is difficult for the operator, seated far above ground level, to always observe the position of the dipper with respect to the tracks and track shoes.
As a consequence, it is too common for an operator to strike a track shoe with the dipper. Shoe and/or dipper damage is likely to occur and damage repair translates to machine downtime and additional diminishment of the return on investment.
And mining shovels are not the only type of earth working machine where good control of the digging implement is highly desired but difficult to achieve. A dragline is also used for mining and, like a shovel, has a platform supported for rotation. Platform support is by what are known as "walk legs" having large, ground-contacting walking "shoes." A machinery house is mounted on the platform and rotates about an axis of rotation which is vertical when the dragline is on level ground. The electrical drive systems used to power various functions of the dragline, i.e., the swing, bucket hoist and bucket retrieval or dragging drives, are mounted in the machinery house. (While the digging implement of a mining shovel is referred to as a "dipper," the digging implement of a dragline is known as a "bucket.")
Extending from the machinery house is a long upwardly, forwardly-pointing angled boom supported by steel cables or lines and in normal operation, the boom angle does not change. The drag bucket is suspended from the boom by other lines and is oriented so that the bucket teeth face rearwardly, i.e., toward the machinery house. The bucket may be raised or lowered by operating the hoist drive. The dragline also has a winch with a rope-like steel cable attached to the bucket. When the winch is powered in a direction to retrieve cable, the bucket is dragged along the ground and drawn toward the machinery house.
In operation, the empty bucket is cast or "tossed" to a point away from the machinery house. Then the dragging winch and the hoist are operated in coordination to move the bucket along a particular contour using a combination of dragging and hoisting motion. For substantially the same reasons as described above, It is difficult for the operator to manipulate the control levers to achieve a particular grade contour.
And that is not the only control problem presented by a dragline. After the bucket is filled, it is hoisted while the machinery upper portion and boom are being swung to one side or the other. When the bucket is properly positioned directly above the "spoil pile" (which may be over 100 feet, about 30 meters, high), the bucket is emptied. While difficult, "spotting" the bucket directly over the pile is important to obtain the greatest pile volume per unit of land area occupied by the pile.
A new method and system for controlling movement of a digging dipper on a mining shovel or a bucket on a dragline and, optionally, for preventing or at least reducing dipper and track shoe damage in a mining shovel would be an important advance in the art.